mysql> select * from table_a ;
+------+--------+-----------------+
| id   | mailid | address         |
+------+--------+-----------------+
|   11 |      1 | tung@email.com  |
|   12 |      2 | jason@email.com |
|   13 |      3 | NULL            |
|   14 |      4 | aa@email.com    |
|   15 |      5 | bb@email.com    |
|   16 |      6 | cc@email.com    |
+------+--------+-----------------+
6 rows in set (0.00 sec)

mysql> select * from table_b ;
+------+--------+------+
| id   | mailid | code |
+------+--------+------+
|    1 |      1 | aa   |
|    2 |      2 | bb   |
|    3 |      3 | ccc  |
+------+--------+------+
3 rows in set (0.00 sec)

mysql> select table_a.id, table_a.mailid, address, code from table_a
    -> left outer join table_b on table_b.mailid = table_a.mailid
    -> ;
+------+--------+-----------------+------+
| id   | mailid | address         | code |
+------+--------+-----------------+------+
|   11 |      1 | tung@email.com  | aa   |
|   12 |      2 | jason@email.com | bb   |
|   13 |      3 | NULL            | ccc  |
|   14 |      4 | aa@email.com    | NULL |
|   15 |      5 | bb@email.com    | NULL |
|   16 |      6 | cc@email.com    | NULL |
+------+--------+-----------------+------+
6 rows in set (0.01 sec)

mysql>